Method for producing a shaft and a device containing a shaft of this type

ABSTRACT

The invention relates to a method for producing a shaft ( 22 ), and an apparatus containing such a shaft ( 22 ), in particular an armature shaft ( 22 ) of an electric motor-driven drive ( 12 ) that is brought to a nominal dimension ( 44 ). The shaft ( 22 ) is reshaped by means of material displacement ( 46 ) at least one point until the nominal dimension ( 44 ) is reached.

CROSS REFERENCE TO RELATED DOCUMENTS

This application is a 371 of PCT/DE01/00497, filed Feb. 9, 2001, whichclaims the benefit of German Patent Applications: No. 100 09 053.2,filed Feb. 28, 2000 and No. 100 30 353.6, filed Jun. 21. 2000.

BACKGROUND OF THE INVENTION

The invention relates to a method for producing a shaft, and anapparatus containing such a shaft.

An apparatus was made known in the German utility-model patent GM 297 02525.2 that is used, for example, to move window panes, sunroofs, orseats. In order to prevent an undesired axial end play of the armatureshaft, it is proposed there that a damper rubber be pressed into arecess of the housing on at least one of its faces. The armature shaftpresses a stop disk against this damping rubber. By means of the firmlylocking into position and the elastic properties of the damping rubber,the armature shaft remains firmly fixed in place despite ageingprocesses and signs of wear. Additionally, the armature shaft can beinstalled very easily and cost-effectively together with the dampingrubber. However, the elimination of the axial end play of the armatureby means of such a damping rubber limits the maximally permissibletolerance in the production of the armature shaft. Narrower toleranceslead to higher production costs, however, which are undesired in a massproduction of the armature shaft.

SUMMARY OF THE INVENTION

The method according to the invention has the advantage that thefavorable offset of end play with the damping rubber can continue to beused even when the shaft is fabricated not very exact to length inproduction. By introducing an additional working step, themanufacturing-related length of the shaft subject to tolerance can bedecoupled from the elimination of the end play of the shaft. This alsomakes a very cost-effective and simple manufacture of the endless screwon the armature shaft possible. The end play is suppressed even morereliably as compared with earlier means for attaining the object of theinvention, because the tolerance stack-ups are markedly lower after thematerial displacement than before. The useful We of the armature shaftis increased as a result and clicking noises produced when the directionof rotation changes are reliably prevented.

If the material displacement takes place near an end of the shaft, thestability of the shaft across the entire length is largely maintained.Additionally, the material displacement at this point does not take upany additional space. If the material displacement is carried out bymeans of burnishing, this is a cost-effective, exact and easy-to-useprocess. Burnishing brings about a continuous elongation of the shaftthat can be well-controlled. The burnishing results in an evenconstriction, which also has a very advantageous effect on the stabilityof the shaft. It is also possible to achieve the material displacementsimply by means of squeezing, however. Such a working step is lessexpensive than burnishing, but it does not entirely achieve the samedimensional accuracy.

If the length of the shaft is measured during the material displacement,the nominal dimension of the shaft can be achieved rapidly and exactlyin one working cycle.

It proves to be particularly favorable when the shaft is installed inthe pole well of the electric motor before the material displacement isstarted. The tolerances that are stacking up are eliminated as a result.Moreover, the armature shaft then lies in “its” bearings, so that thedimensional accuracy and the position of the material displacement canbe coordinated with the eventual site of application, particularly whenburnishing the material displacement.

It is advantageous to measure the length of the part of the installedshaft extending over the pole well, because the shaft can then beproduced to the nominal dimension in the installed state. As a result,the tolerance stack-up of the end play can be markedly reduced.

A further alternative is to measure the set value for the end playduring material displacement with the shaft in the installed state. Thishas the advantage that the measured value of greatest interest—the endplay—can be measured directly and it can be adjusted exactly to the setvalue by means of the material displacement. With this method, allmanufacturing and fitting tolerances are completely eliminated.

Efficient process engineering is a further advantage of materialdisplacement by means of burnishing. The endless screw of the armatureshaft can be produced and the material displacement can be carried outusing just one tool. Even if one tool each is used for the burnishing ofthe endless screw and the burnishing of the material displacement, onecomplete working step is spared, because the shaft need be chucked onlyonce for this process. This makes rapid and cost-effective productionpossible.

The apparatus according to the invention having the features of theindependent claim 9 has the advantage that a high-quality product withnarrow tolerances is created despite initially great productiontolerances of the shaft after installation.

The material displacement located at the end of the shaft and thesemicircular cross-sectional area of the circumferential groove have anadvantageous effect on the preservation of stability of the shaft. It isadvantageous that the shaft diameter can be reduced up to one-half ofthe original value.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of an apparatus according to the invention ispresented in the diagram, and it is explained in greater detail in thesubsequent description. FIG. 1 shows a sectional drawing of anapparatus, and FIG. 2 shows an enlarged section of the shaft accordingto II in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An adjusting drive 10 is shown in FIG. 1 that comprises a motor 12 and amultisectional housing 16 enclosing a gear 14. The motor 12 iselectrically commutated and comprises an armature 18, a commutator 20,and an armature shaft 22 supported in bearings in multiple locationsthat extends into the region of the gear 14. An endless screw 26 thatcommunicates with a worm gear 24 is rolled onto the armature shaft 22.This is supported at the faces 28 and 30 of the armature shaft 22 viastop disks 32 and 34 and at the housing 16 or a part of the housing 16via a damping means 36.

The housing 16 comprises a recess 38 in the region of the face 28 of thearmature shaft 22, into which a damping rubber 40 is pressed as dampingmeans 36. The damping rubber 40 comprises a firmly specified elasticregion 42. The conception according to the invention therefore consistsof the fact that the tolerances of the armature shaft 22 and the housingparts 16, together with the assembly tolerances, may not exceed thedimension of the elastic region 42 (refer to FIG. 2), in order toeffectively prevent play in the armature shaft. Instead of the dampingrubber 40, other damping means 36 such as spring elements or rigid stopsare feasible as well.

In order to adhere to such a narrow tolerance, according to theinvention, the shaft 22 is brought to a nominal dimension 44 by means ofmaterial displacement 46 after the endless screw 26 is rolled on. Thetolerance of this nominal dimension 44 is markedly smaller than theelastic region 42 of the damping rubber 40. The material displacement 46is realized by constricting the shaft 22, by way of which the shaft 22increases. The material displacement 46 is applied to one end region 29between the endless screw 26 and the face 28 in a region where the shaft22 is not radially supported in bearings.

Methods of material displacement 46 are also feasible in which the shaft22 is swaged, which would result in a shortening of the shaft 22.Theoretically, there are a plurality of points on the shaft 22 where amaterial displacement would not disturb the structure. In order tomaintain the overall stability of the shaft 22, however, it presentsitself to displace material on the ends 29, 31 of the shaft 22 in theregion toward their faces 28, 30.

A simple method for material displacement 46 is given by the burnishingof the shaft 22 on its end 29. This method is to be preferred overothers because a burnishing device 54 must be held in front anyway inorder to produce the endless screw 26 on the armature shaft 22. Theburnishing for material displacement 46 can thereby be carried out inone working step, i.e., simultaneously with the burnishing of theendless screw 26, or one directly after the other during one chucking onthe burnishing machine 54.

The length of the shaft 22 is measured simultaneously during thematerial displacement 46. The shaft 22 is deformed until the lengthmeasurement of the armature shaft 22 shows the nominal dimension 44. Thenominal dimension 44 is thereby based on the entire length of thearmature shaft 22 between its two faces 28, 30.

In a second exemplary embodiment, the armature shaft 22 is installed ina part of the housing 16—in a pole well housing 13 in this case—beforeits length is changed. The part of the armature shaft 22 extending overthe pole well 13 is thereby measured simultaneously during its materialdisplacement 46. In this case, the nominal dimension 44′ (FIG. 1) isonly based on the part of the armature shaft 22 extending out over thepole well 13. The tolerances of the field frame 13 can thereby beeliminated as well.

In a further exemplary embodiment, the length of the armature 22 is notmeasured as a nominal dimension 44, but rather, the axial end play 44″(indicated in FIG. 2 with a dotted line) of the shaft 22 is measureddirectly in its installed state. After the armature shaft 22 iscompletely installed and the housing 16 is fully assembled, the materialdisplacement 46 of the armature shaft 22 is thereby carried out via oneor more openings in the housing 16. The armature axial end play 44″ ismeasured by means of an electric voltage or the current drawn by theelectric motor that is applied to the electric motor 12. If the end playis great, the motor 12 reaches its final speed already at relatively lowamperage. If the length of the armature shaft 22 is now extended duringthe current measurement in this case, the armature shaft 22 pressesaxially against the damping rubber 40 at any time. As soon as the shaft22 touches the damping rubber 40, a certain braking torque is producedthat can be measured via an increase in current or a decrease in speedof the motor 12. If the current and/or the speed reach certain values,this is an indication that the end play has been eliminated or stoppedin predetermined fashion.

FIG. 2 shows the material displacement 46 on the end 29 of the armatureshaft 22 in detail. The material displacement 46 is shaped in the formof a ring groove, i.e., encircling the entire shaft. Such a groove 48 iseasy to produce by means of burnishing. The cross-sectional area 50 ofthe groove 48 is semicircular, i.e., the more the shaft 22 must beelongated, the deeper a segment of a circle is pressed into the shaft.It must be ensured that the cross-section 50 of the shaft 22 is notreduced to too great of an extent at the point of material displacement46. A reduction of the shaft diameter 52 to 50% of the original value isregarded as the limit value.

In further exemplary embodiments, the cross-sectional area 50 of thering-shaped groove 48 has a form other than a semicircular form. This isthe case, for example, when the burnishing tool 54 is not shapedradially, but rather takes on another, random shape. Possible shapes ofthe cross-sectional area 50 are a trapezoid 50′ or a rectangle 50″(dotted lines in FIG. 2). With such a profile, more material isdisplaced along one side of the trapezoid or rectangle from thebeginning onward during burnishing, while little material is displacedat the beginning with a semicircular profile of the groove 48.

It is also feasible that the groove 48 is not ring-shaped around theentire circumference of the shaft 22, but rather comprises one or morenotches distributed around the circumference, for example. Such a methodcreates difficulties, however, with regard for a precise nominaldimension 44 of the shaft 44, or it can produce unbalanced states. Theselection of the exact point of material displacement 46 is variablebetween the face 28 and the start of the endless screw 26 on the motorshaft 22.

What is claimed is:
 1. A method for producing an armature shaft (22) ofan electric motor-driven drive (10) in order to prevent an undesiredaxial end play having a nominal dimension (44), the method comprisingthe following steps: reshaping the shaft (22) at least one point bymeans of material displacement (46) until reaching the nominal dimension(44), wherein the material displacement includes constricting the shaft(22) in order to prevent an undesired axial end play, whereby a lengthof the shaft (22) is increased.
 2. The method according to claim 1,wherein the material is displaced by burnishing the shaft (22).
 3. Themethod according to claim 1, further comprising the steps of measuring alength of the shaft (22) during material displacement (46) andterminating the material displacement (46) upon reaching the specifiednominal dimension (44).
 4. The method according to one claim 1, furthercomprising the step of installing the shaft (22) in a pole well (13) ofan electric motor (12) prior to performing the material displacement(46).
 5. The method according to claim 1, further comprising the stepsof measuring a length of a part of the shaft (22) extending over thepole well (13) and comparing the length with the nominal dimension (44).6. The method according to claim 1, further comprising the steps ofmeasuring an end play of the shaft (22) during material displacement(46) and terminating the material displacement (46) upon reaching an endplay set value.
 7. The method according to claim 1, further comprisingthe steps of rolling an endless screw (26) on the shaft (22) on onesection and performing the material displacement (46) up to the nominaldimension (44) simultaneously or afterward at least section-by-sectionon a same machine tool.